using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ConsoleApp2
{
    class Program
    {
        static void Main(string[] args)
        {
           double a = 3.14;

            
            Console.WriteLine("请输入圆的半径");
            double b = double.Parse(Console.ReadLine());
            Console.WriteLine(a * b * b);
            Console.ReadKey();

        }
    }
}
